The complex of polyoma virus middle-T antigen and pp60c-src.

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Abstract
We have recently proposed that the transforming protein of polyoma virus, middle‐T antigen, forms a complex with pp60c‐src. Here we provide additional evidence for the existence of the complex using both monoclonal antibodies specific for middle‐T and antibodies raised against synthetic peptides corresponding to sequences from both middle‐T and pp60c‐src. The complex was retained during partial purification of middle‐T and was stable to incubation under various conditions. A survey of a number of mutants of middle‐T antigen showed that there was a complete correlation between the ability of middle‐T to accept phosphate in the in vitro kinase reaction and the presence of a middle‐T: pp60c‐src complex. This result is in accord with our hypothesis that middle‐T itself is not a protein kinase but rather that pp60c‐src phosphorylates middle‐T. All mutant forms of middle‐T antigen capable of transformation had associated pp60c‐src. The middle‐T of two non‐transforming mutants (hr‐t mutants) did not have associated pp60c‐src, whereas other non‐transforming middle‐T species did associate with pp60c‐src. We propose that the complex plays an essential role in transformation by polyoma virus, but that the existence of the complex per se may not be sufficient.